Reconstruction talk:Proto-Slavic/porzdьnъ

Relation with OCS праздьникъ (holiday)?
Does anyone know what is the relation of this adjective to the Church Slavonic word for holiday праздьникъ? I think it is safe to say that two are related, the question is in what direction? Morphologically, it appears that праздьникъ < *porz- /through, over/ + *dьnь /day/ was the original, however, semantically, it is more likely that the adjective gave rise to the noun. In the later case, though, I am not sure what morphemes could have yielded the observed form (probably *por- /for/ + *sd- /to sit/ or something weird of this sort). Any clues?